we have customized the source code of k2 in version 2.2 now we want to
update the version 2.3 with out affecting our old changes in k2

our web using k2(2.2)
url : www.jorritsmink.com/

can you please suggest regarding this issue

Back up first!
If you modified core field they will be overwritten and have to be re-modified.
If you used template overrides you can most likely use them as is or with a little tweaking
Again, back up first or you may loose data